We have derived the approximate sampling variance of the estimate of variance explained by all common SNPs () for a quantitative trait or case-control study of a disease, and genetic correlation () between two quantitative traits, between two diseases, or between a quantitative trait and a disease, using genome-wide SNP data in unrelated individuals. We believe that the derivations and the online tool will be helpful for researchers to determine how many samples are required to detect (or ) and to estimate (or ) with adequate precision before collecting the genotype data.
